With the development of science, the living standard of human life grows swiftly. Many families have movie theaters at home to entertain themselves. A projector is one of the essential apparatuses to construct a home-movie theater.
FIG. 1 schematically shows the skeleton of a conventional projector. A light beam 11 from a light source is projected to a spectroscope 131 through a polarization beam splitter 12 (PBS) and a lens array 121. The first spectroscope 131 only allows the red light beam R to pass through but reflects the green light beam G and the blue light beam B. The reflected green and blue light beams G, B will be resolved by the second spectroscope 132. The second spectroscope 132 allows the blue light beam B to pass through and reflects the green light beam G. Therefore, as shown in FIG. 1, after the three basic light beams R, G, B are resolved and reflected by spectroscopes 131, 132 and mirrors 141, 142, 143, they enter into an optical combiner 17 from three different directions. The optical combiner 17 is a prismatic combiner, so called an X-cube. The X-cube 17 is used for refracting the three basic light beams R, G, B from three directions toward one direction. i.e. the direction of a focus plate 19.
Before the three basic light beams R, G, B enter into the X-cube 17, each of them will pass through two polarizers 15, 16. These two polarizers 15, 16 are used for adjusting the amount of a light beam (R, G, or B) entering the X-cube 17. After the three basic light beam R, G, B are refracted toward the direction of the focus plate 19, they are mixed as a mixed light beam 20 to be projected on the focus plate 19 by a projection lens system 18. The second polarizer 16 is usually assembled with the X-cube 17. After the X-cube is manufactured, the second polarizer 16 needs to be adjusted to ensure that the three basic light beam R, G, B can be perfectly projected on the focus plate 19 in an equal distance.
FIG. 2 schematically shows a conventional optically adjusting device. The adjusting device includes a frame 22 for fixing an X-cube 17 therein. There are three-layer metal plates 221, outside the frame 22. The second polarizer 16 (not shown) is fixed on the outmost metal plate 221. By adjusting screws 221, 212, 213, 214 and screw hole 215 on the adjusting device, the position and orientation of the second polarizer 16 are adjusted so that the vector parameters of the light beams (including horizontal vector x, vertical vector y, depth vector z, spin vector .theta., and tilt vector .psi.) are adjusted to ensure that the three basic light beams R, G, B can be perfectly projected on the focus plate 19 in an equal distance.
However, the conventional adjusting device still has many drawbacks. Some of them are described as follows:
1. The structure of the conventional adjusting device is very complex. The conventional adjusting device needs multi-layer metal plates to accomplish the adjustment thereby resulting in a difficulty in the manufacturing process and increasing the manufacturing cost. PA1 2. A lot of heat will be generated from the polarizers when light beam are reflected thereon, but the conventional adjusting device can not dissipate heat easily because of its complex structure.